The present invention relates to a device for preventing a fixing nut, screw or bolt from being loosened, adapted to be used in particular, but not exclusively, as an anti-theft device for a wheel of an automobile vehicle.
Anti-theft devices are already known which are intended to prevent dismantling by a third party of a wheel of an automobile vehicle. Certain of these of these devices employ a special lock nut which is itself capped by a cylindrical cap which may be rendered fast with the special nut by means actuated by a spanner. Other devices of this type use a locking mechanism comprising lugs displaced magnetically. All these devices present the drawback of requiring the use of a special nut in place of a standard lock nut.
Other anti-theft devices employ an intermediate sleeve which is locked in a non-removable manner on one of the fixing nuts and of which the front face presents a combination of hollows adapted to receive catches of an unlocking spanner. These catches are disposed on the spanner in the same manner as the hollows on the intermediate sleeve in order to be able to engage in these hollows and drive in rotation the intermediate sleeve and the lock nut which is fast therewith when the unlocking spanner is rotated.
Such a device presents the drawback of being relatively expensive and of using the intermediate sleeve as an effort transmitting member when tightening and loosening the lock nut.
A device of this type is also known at the present time in which, between the cap and the fixing nut, screw or bolt, there is interposed a longitudinally slit intermediate bush, of polygonal internal cross section, identical to the outer profile of the nut or head of the fixing screw or bolt, the cylindrical outer lateral surface of the intermediate bush presenting, over part of its height, a thread identical to that of the cap. In this way, if this intermediate bush is crushed on the nut or head of the fixing screw or bolt, any possibility of axial withdrawal of the cap is prevented.
The device of this type has proved fairly efficient, but it presents the major drawback of comprising said intermediate bush which is a member difficult to manufacture and which risks being lost or soiled, which renders the device unusable.